Particulate filters may reduce the amount of particulate matter emissions (also referred to as soot) released by an engine by trapping the particles in the exhaust system of the engine. Particulate filters are typically regenerated during operation of the engine to decrease the amount of trapped particulate matter. For example, regeneration may be performed by raising the temperature of the filter to a predetermined temperature, and ensuring that the exhaust gas entering the particulate filter is of a certain composition. To achieve this, fuel may be injected into the exhaust stream after a main combustion event. The post-combustion injected fuel is combusted over catalysts placed along the exhaust stream. The heat released during the fuel combustion on the catalysts increases the exhaust temperature, which burns the trapped particles in the filter. However, the above-described approach increases fuel consumption and can result in a higher temperature increase in the exhaust system than desired, which may be detrimental to the exhaust system components, including the particulate filter. Further, because this temperature increase in the exhaust gas is typically above the efficient operating window for exhaust aftertreatment systems, the NOx emissions typically increase during this time because the aftertreatment system is unable to completely reduce the NOx that was formed in-cylinder. Thus, both the emissions and the fuel consumption are increased during regeneration over what occurs during normal operation.
Other attempts to address particulate filter regeneration include utilizing an electrically-operated heater at the particulate filter rather than relying on fuel-based temperature control. One example approach is shown by Gonze et al. in U.S. Patent Application Publication No. 2013/0291515. Therein, an electric heater disposed upstream of a particulate filter is selectively energized during an engine-off condition to heat the particulate filter for regeneration. A pump positioned in the exhaust system is also activated to draw ambient air through the particulate filter during regeneration.
However, the inventors herein have recognized potential issues with such systems. As one example, air flow through the particulate filter during regeneration is controlled only by the displacement of the pump, and conditions of the particulate filter during regeneration are not monitored. As such, this uncontrolled regeneration may lead to overheating at the particulate filter, which may degrade the filter, at least in some examples. In other examples, the uncontrolled regeneration may lead to regeneration events where insufficient heat is provided to the particulate filter to effectively perform the regeneration. Further, by energizing the heater via the vehicle battery or batteries, stored energy needed to start the engine on a subsequent engine start may be compromised and/or complex energy monitoring and supply schemes may be enacted to ensure sufficient charge is available in the batteries prior to initiating the regeneration.
In one example, the issues described above may be addressed by a method including, during a non-engine operating condition, regenerating a particulate filter coupled in an exhaust system downstream of an engine by activating an electric heater of the particulate filter and directing intake air through the particulate filter, the intake air bypassing the engine, and adjusting an electrical load of the electric heater responsive to one or more of exhaust temperature and intake airflow.
In this way, the air flow provided to the particulate filter during the regeneration may be drawn in through the intake system of the engine and to the exhaust system, bypassing the engine. By doing so, the air may flow past various sensors, such as an intake mass air flow sensor, an exhaust temperature sensor, and/or other sensors. Using the output from the sensors, the electrical load of the electric heater may be adjusted to maintain a target particulate filter temperature during the regeneration. Additionally, the output from the sensors may be used to modulate the air flow provided to the particulate filter to maintain temperature for a given heater electrical current. Thus, the electric heater may be used to perform the regeneration while still relying on various engine sensors to control the regeneration, thereby lowering fuel consumption and avoiding uncontrolled regeneration of the particulate filter. Further, at least in some examples, the electric heater may be supplied energy from a remote power source, such as a power grid, rather than the vehicle battery, and thus regeneration may occur without regard for vehicle battery state of charge.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.